1. Field of the Invention
The present invention relates to a Hg-based 1223-type oxide superconductor which exhibits superconductive properties at a temperature higher than liquid nitrogen temperature, and a method of manufacturing the oxide superconductor.
2. Description of the Related Art
Superconductors have unique properties, in which the electric resistance is rendered zero at a critical temperature (to be abbreviated as Tc, hereinafter), the diamagnetism and Josephson effect are exhibited. The superconductors are expected to be applied in a wide range of technological field including power cables without current loss, superconducting generator, high field magnets for nuclear fusion plasma confinement, materials for magnetic levitation vehicle, magnetic sealed materials, and high-speed computers.
It is reported that the superconducting properties have been confirmed in about 30 types of copper oxides after the discovery of the La-Ba-Cu-O-based superconductor having Tc of about 30K in 1986 by Bednorz and Muller. In particular, the Tl-Ba-Ca-Cu-O-based superconductor has a Tc of 125K, and much attention is paid thereto as a material having the highest Tc ever. Recently, it has been reported that the Hg-Ba-Ca-Cu-O-based superconductor (1223 type) exhibits a Tc of 133.5K (A. Schiling et al., Nature (London) 363.56 (1993).
The Hg-Ba-Ca-Cu-O-based superconductor is prepared in the following method. First, the precursor e.g., Ba.sub.2 Ca.sub.2 Cu.sub.3 O.sub.7, BaCuO.sub.2, Ca.sub.2 CuO.sub.3 or other oxides is prepared, and HgO is mixed thereinto. The mixture is further subjected to a thermal treatment at a temperature of 800.degree.-850.degree. C., for 10 hours, thus obtaining the superconductor.
However, the Hg-Ba-Ca-Cu-O-based superconductor entails problems, i.e. it contains mercury which is poisonous, it requires much time in its production since HgO must be mixed with the precursor, and it has a low reproducibility. Further, the crystal structure of the Hg-Ba-Ca-Cu-O-based superconductor has a large anisotropy, and therefore it is expected that the superconductive properties including the critical current density in a magnetic field, are very low.